Used in medium

01.define_module.rb

module Test
  def self.hellow
    puts "I'm a module method."
  end

  def hello
    puts "I'm an instance method."
  end
end

02.access_module.rb

# => call required file without extension .rb
require_relative '01.define_module'

# call methods 1st way
extend Test
# access module method
Test::hellow  # => I'm a module method.
hellow  # => undefined local variable or method `hellow' for main:Object (NameError)
# access instance method
Test::hello   # => undefined method `hello' for Test:Module (NoMethodError)
hello  # => I'm an instance method.

# ---------------------------------------------------------------------------- #

# call methods 2nd way
include Test
# access module method
Test::hellow  # => I'm a module method.
hellow  # => undefined local variable or method `hellow' for main:Object (NameError)
# access instance method
Test::hello  # => I'm an instance method.
hello         # =>  I'm an instance method.